The advantage of using a continuous probability density function to
model a set of statistical data is that instead of having to do
calculations with all the separate values we can use calculus to
find the required results.
The median is the point $t$
in the interval such that $$\text{Prob}\{0 \leq X \leq t\} =
\text{Prob}\{t \leq X \leq 3\}$$
The mean of the
distribution is $m$, where $$m=\int_0^3x\,\rho(x)\,dx.$$
In a discrete distribution the mode is the value that occurs most
frequently. In a continuous distribution it is the value where the
probability density function takes its maximum value.